The ideal electrophoresis procedure, particularly in capillaries, is one in which the resolution of the solute zones is not lessened by either electroendosmosis or solute adsorption at the wall of the capillary or other electrophoresis chamber. If the effect of electroendosmosis were to produce a perfect plug flow, the only result would be a displacement of the solute zones with no effect on resolution. Electroendosmosis has, however, been found to cause zone deformation and a loss of resolution. With capillaries whose inner wall surfaces have been coated with a polymer to suppress electroendosmosis, it has also been noticed that the solute zones broaden with repeated use of the capillary. One explanation is the gradual deterioration of the coating upon exposure to the high pH conditions involved in electrophoretic procedures. An alternative explanation is solute adsorption by the coating upon repeated use. The adsorbed solutes place charges on the wall surface, the charges themselves giving rise to electroendosmosis.
Hjerten, U.S. Pat. No. 4,680,201, Jul. 14, 1987, discloses the application of a thin coating of an uncharged polymer to the capillary wall. The polymer commonly used for this purpose is linear polyacrylamide, and the effect of the polymer coating is to eliminate electroendosmosis and suppress adsorption. Experiments have shown that the polyacrylamide coating is stable for at least four weeks (the test period) at pH 11, but for only a few hours at pH 12. The reason is that acrylamide bonds tend to hydrolyze at high pH. The ability to withstand high pH conditions is important since wash solutions at pH 12-13 are needed for releasing adsorbed solutes.
This and other problems encountered in the prior art are addressed by the present invention.